Electric motors represent a substantial capital investment in industrial operations. When a motor fails, the associated costs from repairs pale in comparison to the financial impact of unplanned downtime and lost productivity. Studies suggest that downtime costs can exceed repair expenses by up to 10x, emphasising the urgency of swift yet thorough failure analysis.
Identifying the root cause of motor failure is critical to preventing recurrence and enhancing operational reliability. Whether conducted in-house by maintenance teams or outsourced to specialised contractors, a systematic investigation is indispensable. Bearing failures alone account for 51–65% of motor breakdowns, according to industry data, making them a primary focus during inspections.
The Role of Bearing Inspections in Motor Reliability
A comprehensive bearing inspection provides actionable insights to guide repair strategies, whether through localised fixes, electric motor or generator overhauls, or component replacement. Addressing root causes—such as improper lubrication, contamination, or electrical damage—can extend motor lifespan and reduce future downtime.
For standardised procedures, consult resources like the AEGIS Handbook, which outlines best practices for bearing inspection and failure prevention. Pairing these guidelines with expert analysis ensures accuracy, particularly when dealing with complex issues like electrical discharge machining (EDM) damage. Before starting the process, always prioritise safety: de-energise the motor, lock-out/tag out (LOTO) systems, and use PPE before beginning inspections.
Key Bearing Inspection Methods and Indicators
1. Visual Inspection
Start by removing protective covers to examine bearings for:
- Discolouration: Bluish hues on rollers or races signal overheating from excessive friction or electrical arcing.
- Rust/Corrosion: Moisture ingress or chemical exposure compromises bearing integrity.
- Cracks or Spalling: Fractures on rolling elements or raceways indicate mechanical fatigue.
- Lubricant Leakage: Failed seals or degraded grease lead to inadequate lubrication.
- Contamination: Particulate ingress accelerates wear; inspect for dirt, dust, or metal shavings.
- EDM Damage: Microscopic pitting (5–10µm) from shaft voltage discharges, common in VFD-driven motors without bearing protection. Over time, EDM progresses to “frosting” (grey raceway streaks) or “fluting” (washboard-like grooves). Use magnification to differentiate EDM from mechanical wear.
2. Tactile Inspection
Assess bearings during operation (if safe) or manual rotation:
- Vibration Analysis: Use handheld meters to detect abnormal frequencies linked to imbalance or misalignment.
- Temperature Checks: Bearings running >70°C above ambient risk lubricant breakdown.
- Manual Rotation: Roughness or binding suggests brinelling, debris, or raceway damage.
3. Auditory Inspection
Unusual noises often precede failure:
- Grinding/Squealing: Metal-to-metal contact due to lubrication failure.
- Rumbling: Contaminants in the bearing assembly.
- Clicking: Damaged rollers or cage instability.
Note: Acoustic emission sensors can automate this process for critical motors.
4. Lubrication Check
Improper lubrication is among the top causes of bearing failures:
- Grease Consistency: Degraded or hardened grease fails to protect.
- Oil Level: Check sight glasses or dipsticks; top up with manufacturer-approved lubricants.
- Contamination: Use particle counters to assess oil cleanliness in scenarios that involve services like MV motor rewind in Singapore.
5. Shaft Movement Analysis
Measure play with dial indicators:
- Radial Play >0.1mm: Worn rollers or outer raceways.
- Axial Play >0.05mm: Thrust bearing wear or improper preload.
Excessive movement often necessitates replacing bearings and realigning the shafts.
Conclusion
Proactive bearing inspections are a cost-effective strategy to mitigate unplanned downtime and avoid costly repairs or full motor replacements. Conducting the various checks discussed above is key to uncovering failure precursors early before they cause bigger problems. Incorporate these practices into predictive maintenance schedules to enhance reliability, reduce lifecycle costs, and safeguard productivity.